Finale 2014.5 add double bar
EELS line-scan profile indicates the distribution of Au, Pd and Co components in a representative single nanoparticle, where the Pd shell thickness measured is around 0.9–1.2 nm and Au atoms are distributed on the surface. 34), reveals that the intensity profile for Au and Pd is nearly depleted in the centre of the nanoparticle, whereas for Co it is enriched in the centre. 1), whose contrast is directly related to atomic number Z (ref. The high angle annular dark-field images as shown in Fig. We use the AuPdCo annealed at 500 ☌ sample as a reference for the disordered core-shell AuPdCo catalysts. 1a,b, the nanoparticles have a core-shell structure with AuPd atoms on the surface and Co in its core.
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The nanoparticles tend to grow when annealed at 500 ☌ in H 2 for 30 min attaining an average diameter of 4 nm while maintaining their core-shell structure. The structures of the as-obtained core-shell nanoparticles were controlled by annealing at different temperatures under a flowing H 2 gas atmosphere. Initially, core-shell structures of AuPdCo nanoparticles that had an average diameter of 1 nm were obtained using the step-by-step chemical synthesis method (see Methods). The increased activity and durability of the catalyst is accredited to multiple facets and the structural ordering observed in the nanoparticles. Furthermore, microscopic analyses of the catalyst shows that atomic ordering of the nanoparticles can significantly affect the catalytic activity.
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These structurally ordered intermetallic AuPdCo nanoparticles tend to behave similar to Pt catalyst for ORR but more interestingly have much better stability than Pt in alkaline media. To our knowledge, no prior evidence of such intermetallic phases in nanoparticles of PdCo alloy has previously been reported.
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Electron microscopic techniques demonstrate that, at elevated temperatures, palladium cobalt nanoparticles undergo an atomic structural transition from core-shell to a rare intermetallic ordered structure with twin boundaries forming stable facets is revealed using high-resolution transmission electron microscope (HRTEM) and scanning transmission electron microscope (STEM) coupled with electron energy-loss spectroscopy (EELS) and electron diffraction patterns (EDPs). Here we report on a structurally ordered Au 10Pd 40Co 50 catalyst that exhibits comparable activity to conventional platinum catalysts in both acid and alkaline media. Considerable efforts to make palladium and palladium alloys active catalysts and a possible replacement for platinum have had a marginal success.